Organogermanium chemistry is the science of chemical species containing one or more
C–
Ge bonds. Germanium shares
group 14 in the periodic table with carbon,
silicon,
tin and
lead. Historically, organogermanes are considered as
nucleophiles and the reactivity of them is between that of
organosilicon and
organotin compounds. Some organogermanes have enhanced reactivity compared with their organosilicon and
organoboron analogues in some
cross-coupling reactions.[1]
In general, organogermanium chemistry is much less well-developed than the other group-14 congeners, mainly because germanium is expensive.[2]
Synthesis
The great majority of organogermanium compounds are tetrahedral with the formula GeR4-nXn where X = H, Cl, etc. Ge-C bonds are air-stable, although Ge-H bonds can undergo air-oxidation. The first organogermanium compound, tetraethylgermane, synthesized by Winkler in 1887,[3] by the reaction of
germanium tetrachloride with
diethylzinc. More commonly, these Ge(IV) compounds are prepared by alkylation of germanium halides by
organolithium and
Grignard reagents, including surfaces terminated with Ge-Cl bonds.[4] Recent work, however, has developed
chlorine-free germanium processing.
Some organogermanes are prepared by nucleophilic substitution or Pd-catalyzed cross-coupling reactions.[1] Hydrogermylation provides another route to organogermanium compounds.[5]
Catenation
Akin to
hydrocarbons and
polysilanes, many organogermanium compounds are known with Ge-Ge bonds. An early example is hexaphenyldigermane, (C6H5)3Ge−Ge(C6H5)3. It is prepared by
Wurtz coupling of the bromide:[7]
2 (C6H5)3GeBr + 2 Na → (C6H5)3Ge−Ge(C6H5)3 + 2 NaBr
Many cyclic polygermanes are known, e.g. [Ge(C6H5)24, [Ge(C6H5)25, and [Ge(C6H5)26.
Germanols
Triphenylgermanol ((C6H5)3GeOH) is a colorless solid. Like the isostructural
silanol, it engages in hydrogen bonding in the solid-state.[8]
Multiple bonds to Ge
Compounds with multiple bonds to Ge are usually highly reactive or require bulky organic substituents for their isolation. This situation follows from the
double bond rule. Digermynes only exist for extremely bulky substituents. According to
X-ray crystallography, the C–Ge≡Ge–C core of digermynes is bent. Such compounds are prepared by the reduction of bulky arylgermanium(II) halides.[9]
Compounds containing Ge=C (germenes) double bonds require bulky organic substituents for their isolation.[10] and Ge=Ge (digermylenes)[11] Other examples include the bulky derivatives of germabenzene and 1,2-digermabenzene,[12] analogues of benzene.
Germylenes and germanium radicals
Germylenes (carbene analogues) and germyl free radicals have been investigated. Reaction of a Ge(II) chloride with a lithium trialkylgermanide affords a germylene:[13]
ArGeCl + LiGe(C(CH3)3)3 → ArGeGe((C(CH3)3)3 + LiCl (Ar = 2,6-(mesityl)2C6H3)
Some organogermanium compounds participate in cross coupling reactions.
Applications
Organogermanium compounds are used in relatively few commercial applications.
Isobutylgermane, a volatile colorless liquid, is used in
MOVPE (
Metalorganic Vapor Phase
Epitaxy) in the deposition of Ge
semiconductor films.
^Akiyama Takahiko (2004). "Germanium in Organic Synthesis". In Yamamoto Hisashi; Oshima Koichiro (eds.). Main Group Metals in Organic Synthesis.
ISBN3-527-30508-4.
^Buriak, Jillian M. (2002). "Organometallic Chemistry on Silicon and Germanium Surfaces". Chemical Reviews. 102 (5): 1271–1308.
doi:
10.1021/cr000064s.
PMID11996538.
^Sekiguchi, Akira; Yatabe, Tetsuo; Kabuto, Chizuko; Sakurai, Hideki (1993). "Chemistry of organosilicon compounds. 303. The missing hexasilaprismane: Synthesis, x-ray analysis and photochemical reactions". Journal of the American Chemical Society. 115 (13): 5853–5854.
doi:
10.1021/ja00066a075.
^Amadoruge, Monika L.; Weinert, Charles S. (2008). "Singly Bonded Catenated Germanes: Eighty Years of Progress". Chemical Reviews. 108 (10): 4253–4294.
doi:
10.1021/cr800197r.
PMID18816144.
^Setaka, Wataru; Sakamoto, Kenkichi; Kira, Mitsuo; Power, Philip P. (2001). "Synthesis and Structure of Stable Tri-tert-butylgermyl-Substituted Stannylene and Germylene". Organometallics. 20 (22): 4460–4462.
doi:
10.1021/om010591h.